Physiology
Gastrointestinal
Regarding basic gastrointestinal anatomy, which of the following statements is INCORRECT:
Answer:
The submucosal plexus (Meissner's plexus) is located in the submucosal layer. The submucosal plexus only has parasympathetic input and provides secretomotor innervation to the mucosa, mainly regulating epithelial cell and submucosal blood vessel function. The myenteric plexus (Auerbach's plexus) is located between the circular and longitudinal muscle layers of the muscularis externa. The myenteric plexus provides motor innervation to the smooth muscle layers via sympathetic and parasympathetic input, mainly regulating intestinal motility and sphincter function.Structure of Gut Wall
Physiology / Gastrointestinal / Gut Wall
Last Updated: 29th July 2024
The gastrointestinal system is essentially a muscular tube which maintains the same basic structure throughout its length, although this is modified as function varies.
Layers
The layers that comprise this basic structure (from innermost to outermost) are:
- The innermost mucosa composed of:
- the epithelial layer (which has either secretory or absorptive functions)
- the lamina propria (consisting of loose connective tissue, blood vessels and lymph tissues)
- the muscularis mucosa (a thin layer of smooth muscle)
- The submucosa (containing a second layer of connective tissue, larger blood vessels and lymphatic vessels and the submucosal plexus)
- The muscularis externa composed of
- the inner circular muscle layer (which, when it contracts, produces a constriction of the lumen)
- the outer longitudinal muscle layer (which, when it contracts, results in shortening of the GI tract)
- the myenteric plexus which lies between these two layers of muscle
- The outermost serosa (another connective tissue layer covered with squamous mesothelial cells)
Innervation
There are two intrinsic nerve plexuses which function as the enteric nerve system, the activity of which is moderated by extrinsic innervations and hormones.
The submucosal plexus (Meissner's plexus) is located in the submucosal layer. The submucosal plexus only has parasympathetic input and provides secretomotor innervation to the mucosa, mainly regulating epithelial cell and submucosal blood vessel function.
The myenteric plexus (Auerbach's plexus) is located between the circular and longitudinal muscle layers of the muscularis externa. The myenteric plexus provides motor innervation to the smooth muscle layers via sympathetic and parasympathetic input, mainly regulating intestinal motility and sphincter function.
Structure of the Gut Wall. (Image by Goran tek-en [CC BY-SA 3.0 , via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
